9i 



A portion of the CaO and CO2 calculated as calcite is 

 present as cancrinite which is occasionally seen in thin 

 sections in small amount. In calculating the "mode" the 

 nepheline is assumed to have the same chemical composition 

 as it possesses it in the Bancroft district, viz., to contain 

 rather more than 5 per cent of K 2 o. 



3. Raglanite is a white or grey corundiferous nepheline 

 syenite poor in nepheline. The specimen analyzed was 

 chosen as representative of the more highly feldspathic 

 variety of the nepheline syenite of Craigmont. Since 

 that time quarrying operations have exposed still more 

 highly feldspathic phases, which may be referred to as 

 plumasite, a name originally proposed by Dr. Andrew 

 C. Lawson (Bull. Dept. Geol. of California, Vol. Ill, No. 8, 

 pp. 219-229). An analysis of raglanite is given on p. 95. 

 The rock is composed of about 69 per cent of oligoclase, 

 12 per cent of nepheline and 4-45 per cent of corundum, 

 with subordinate amounts of muscovite, biotite, magne- 

 tite, calcite and apatite. 



4. Plumasite is an alkali-syenite made up almost 

 exclusively of white oligoclase with a relatively subordinate 

 amount of corundum. Muscovite, biotite and scapolite 

 are sometimes present as accessory constituents. Plumasite 

 is closely allied to dungannonite.* 



5. Umptekite is the red or pink alkali-syenite and 

 differs from plumasite chiefly by reason of the fact that a 

 considerable quantity of potash feldspar is present. Usually 

 it is distinctly foliated, the structure being marked by 

 minute scales of biotite. An analysis of the rock is given 

 on p. 96. Umptekite is, perhaps, the most abundant 

 representative of this alkali series at Craigmont. Its 

 approximate mineralogical composition is of orthoclase 

 and microcline (30 per cent), albite (55 per cent), magnetite 

 with a little biotite and corundum. Some specimens con- 

 tain small amounts of hornblende or pyroxene as accessory 

 constituents replacing the biotite. 



6. Anorthosite has only recently been recognized in 

 some of the newer workings at Craigmont. It is a coarsely 

 granular rock of greyish or greenish-grey colour. It is 

 composed, essentially, and sometimes almost wholly, of a 

 plagioclase feldspar, having a composition intermediate be- 



*It is to be noted that the feldspar in Lawson's plumasite is highly altered, con- 

 taining 1...7 per cent of water. It has the specific gravity and extinction angles of 

 oligoclase but the composition of andesine. 



